No, It is not mandatory to get Index but it is most important to get a better ranking in Google.
A standard website/blog must have a privacy policy page/terms & conditions page, about us page, contact us page, Copyright Policy Page (If need).
These page will help you to get a good place in search engines as well better page rank.
If you want to monetize your blog using Adsense, then it is most important for your blog/site.